Gαh/transglutaminase-2 activity is required for maximal activation of adenylylcyclase 8 in human and rat glioma cells

G alpha(h) (or transglutaminase-2 (TG2)) is an atypical guanine nucleotide binding-protein that associates with G protein-coupled receptors. TG2 also exerts transglutaminase activity that catalyzes posttranslational protein cross-linking with the formation of epsilon-(gamma-glutamyl) lysine or (gamma-glutamyl) polyamine bonds. Here, the role of G alpha(h)/TG2 in signal transduction in glial cells was examined in detail. In 1321N1 human astrocytoma cells that lack G alpha(h)/TG2, overexpression of G alpha(h)/TG2 caused an enhancement of CAMP accumulation stimulated with the beta-adrenergic receptor agonist, isoproterenol, or the adenylylcyclase activator, forskolin. This cAMP-enhancement was reversed by the TG2 inhibitor, ERW1069. In rat C6 glioma cells that express endogenous G alpha(h)/TG2, cAMP accumulation induced by isoproterenol or forskolin was significantly inhibited by overexpression of G alpha(h)/TG2-C277V, a dominant-negative mutant that lacks transglutaminase activity, but was not inhibited by the G alpha(h)/TG2-S171E mutant that cannot bind GTP/GDP. These results suggest G alpha(h)/TG2 potentiates adenylylcyclase activity by its transglutaminase activity and not by its G-protein activity. G alpha(h)/TG2 also increased the activities of the cAMP response element and interleukin-6 promoter, accompanied by an of cAMP in both glioma cells. Since adenylylcyclase 8 plays a major role in cAMP production, we focused on post-translational modification of adenylylcyclase 8 by G alpha(h)/TG2. Adenylylcyclase 8 is expressed in both 1321N1 and C6 cells; however, G alpha(h)/TG2 affected neither adenylylcyclase 8 expression levels, glycosylation, nor dimerization status. In contrast, pentylamine, a substrate of G alpha(h)/TG2, was incorporated into adenylylcyclase 8 in a transglutaminase activity-dependent manner. Taking these results together, G alpha(h)/TG2 promotes cAMP production accompanied by a modification of adenylylcyclase 8 in glioma cells. (C) 2012 Elsevier Inc. All rights reserved.